The aim of this research project is to synthesize for evaluation as anticancer agents a series of bridgehead nitrogen heterocylces of the purine type. Synthetic procedures involve utilization of cycloaddition reactions of heterocyclic N-ylides with acetylenic and olefinic dipolarophiles, heteroaromatic betaines containing 1,3- and 1,4-dipoles, and also photochemical methods. Five- and six-membered rings, fused together and to each other, as well as larger ring systems, will be included in this study. BIBLIOGRAPHIC REFERENCES: Pulse Fourier Transform C13 Nuclear Magnetic Resonance Spectra of Cyclopropenones and Related Derivatives, M. T. W. Hearn and K. T. Potts, J. C. S. Perkin II, 1918 (1974). Bridgehead Nitrogen Heterocycles. IX. Fused-Ring Systems Derived from Fusion of the 1,2,4-Thiadiazole System with Isoxazole, 1,3,4-Oxadiazole, Thiazole, 1,2,4-Thiadiazole and 1,3,4-Thiadiazole Systems, K. T. Potts and J. Kane, J. Org. Chem., 40, 2600 (1975).